Composition for scale conditioning and lubrication of metals



United States Patent O COMPOSITIGN FOR SCALE CONDITIONING ANDLUBRHCATION OF METALS Robert A. Simon, Seattle, Wash, assignor to NorthAmerican Aviation, Inc.

No Drawing. Application May 27, 1955 Serial No. 511,745

1 Claim. (Cl. 252-25) This invention pertains to a metal conditioningcmposition and more particularly to a composition which conditions scaleon titanium and stainless steel for subsequent removal, and which isadditionally an effective metal working lubricant.

With the advent of titanium and its alloys as production metals numerousproblems have resulted from a metal working standpoint. One of thedifficulties results from the formation of a complex scale on thesurface of titanium metal and its alloys when it has been subjected toheat such as in forming, heat treating or the like. This scale not onlygives a poor appearance but it also interferes with inspectionprocedures, lessens the ductility of the metal and can interfere withwelding. Removal of this scale therefore becomes imperative. It has beenpast practice to use an acid pickling bath to remove the scale after theparts have been subjected to heat. This was a passable solution to theproblem while forming and heat treating of titanium remained atrelatively low temperatures. However, now titanium parts are beingsubjected to temperatures up to 1100 F. and

a heavier scale is formed of such character that all known acid pickleshave proved to be unsatisfactory. In

the first place where a part has been given a scaleat a rel atively hightemperature it is necessary to leave it in the pickle for a considerableperiod of time which becomes a severe penalty from a productionstand-point. Also, the active ingredients in the bath are rapidlydepleted. Even more important, in removing scale in this manner anexcessive amount of metal will be lost so that it becomes impossible tokeep the work piece within prescribed tolerances. As much as percent ofthe thickness of light gauge parts may be lost in descaling.Furthermore, the scale removal will be imperfect over the surface of thepart, considerably more scale being removed from some portions thanothers.

A similar problem has been encountered with the use of 17-7 PH stainlesssteel. This is a precipitation hardening stainless steel containingaround 17% chromium, 7% nickel, and 1% aluminum more fully described inMilitary Specification MIL-S-25043 (ASG). This material may be heated ina typical heat treat cycle to 1900". F. for annealing and cured at 1400P. which provides a severe scale condition on the surface of the partcomprising a magnetic iron oxide material having Fe O in a highproportion. This is a very stable scale which is not attached by anordinary acid bath. It has been attempeted to remove the scale byabrasives, but this too has diificulties not only from the practicalstandpoint of covering the entire area, but also from the degree ofsurface roughness which the abrasives cause. In one instance it wasdesired to resistance weld a 17-7 PH stainless steel part from which thescale had been removed by an abrasive process. The roughness resultingfrom this descaling procedure was so great that resistance weldingbecame impractical because a uniform contact could not be obtained.

The metal bath of this invention is applied to the Patented Mar. 29,1960 ice heating and causes the scale formation to be of such characterthat it can be removed by existing acid baths with relative ease andreliability.

A metal working lubricant obviously must possess the basic qualitieswhich enable it to so protect the part and die during a formingoperation so that there is no damage to either. For this purpose it mustbe adherent and tough. Also it should be simple to handle and apply, andpreferably can be applied to the part prior to its introduction into thearea of a press where the part was to be formed. This will keep thepress area clear and allow the lubricant to be applied in a more orderlymanner. Ideally the material used as a lubricant should also form adurable coat which will protect the part during its handling. Removal isthe next major problem, which for metal working lubricants generallyinvolves scrubbing with suitable solvents. The bath of this inventionprovides a metal working lubricant which answers all of theserequirements. It is not only extremely effective for room temperatureforming operations but provides a tough protective film which may beapplied long before the part is formed. Removal of the lubricantinvolves only dipping of the part in water whereupon it will all bedissolved and the part will be clean.

Accordingly, it is an object of this invention to provide a materialwhich will condition scale formations so as to permit subsequentcomplete scale removal from a short dip in a conventional acid picklebath. Addition ally, it is an object of this invention to providea'condi-- .tioning material which is easily applied and removed, andgives protection to a workpiece during handling. A further object ofthis invention is to provide a materialeffective as a metal workinglubricant which will protect" part and die during a forming operation.Yet another object of this invention is to provide a single material:serving the functions of part protection, lubrication for forming, andconditioning for scale formations obtained when the part is heated.These and other objects will become apparent from the following detaileddescription. I l Considering first the problem of a pretreatment forminimizing scale and permitting it to be readily removedsubsequent toheating, I have found that basically the results may be obtained byapplying borate or a boron bearing material to the titanium or 17-7 PHstainless steel prior to its being subjected to high temperature.

This will so condition the scale which is formed so that. it can beremoved without ditficulty. No problem ofhydrogen absorption isencountered with the compound of this invention.

A particular composition which has proven to be successful is asfollows:

Component: Percent by weight Boric acid, tech. '7.8-to 8.2 Shellac,orange flake 4.0 to 4.5 Diethylamine, tech. 3.3 to 3.5 1 Dye .05 to .06Water, distilled or deionized 4.0 to 5.0

Methanol, Federal Spec. O.M232, Remainder The boric acid contained inthe substance of the above the scale formation.

lyze into boric acid and therefore may replace that ingredient.

Boron bearing materials containing potassium, and sodium have been foundto be harmful to, titanium;

3 when it is subsequently subjected to heat. Consequently they shouldnot be used in a pretreatment compound.

The shellac is included primarily to serve as a binder. For this purposealone it might be satisfactory to use another type of binder such as,for example, varnish. However, shellac is chosen because it has someeffect of its own in modifying the scale formation so as to permit thesubsequent removal thereof.

The ammonia carrying compound, diethylamine, is mainly to give thesolution water solubility. Ammonium hydroxide may be used in lieu of thediethylamine, but results in a material not quite as stable as when thelatter substance is included. Ethylene diamine may also be substitutedfor diethylamine. The ammonium carrying material used should have arelatively low boiling point and be a strong base readily yielding itsammonia radical. Heavier materials will become gummy rather thanproperly drying out. Other bases such as sodium, potassium and calciumhydroxides actually have'a harmful effect on the metal and cause spotswhich cannot later be pickled off.

The primary purpose of the methanol is to act as a solvent. The water inthe solution serves to hydrolyze the methyl borate that is formed withthe boric acid, preventing its loss. Therefore, when the composition isprepared it is important to combine the water and methanol before addingthe boric acid. Because sodium or potassium salts have a deleteriouseffect on titanium when subsequently heated, it is necessary to usedistilled ordeionized water.

Ethanol may be employed in the composition as a substitute for themethanol with no loss in desirable characteristics. The use of ethanolavoids the toxicity which is present when methanol is used. Commercialethanol contains around five percent water, so further addition of waterto the composition is unnecessary when this material is used.Isopropanol is also acceptable. Heavier alcohols, however, have agreater drying time and for that reason are not as desirable for use inthe compound. The main advantage of methanol is that more boric acidwill go into solution therein than into these other alcohols.

The dye in the composition serves merely 'as an indicator giving thecompound enough color so that it is possible to determine exactly whatportions of the part have been covered. Any suitable alcohol soluble dyemay be used.

The material so prepared may be applied in any desired manner such asbrushing, dipping or spraying, with the latter generally proving moreconvenient. The result is'a coating which is adherent and tough so thatthe part receives protection prior to the heat treating operation, andwhich also assures that there is little likelihood of losing the coatingfrom the surface of the part.

As far as the proportions indicated for the solution are concerned somevariation may be permitted, but the range indicated represents what isbelieved to be an optimum condition for the ingredients included. Theacid, being the primary agent for conditioning the scale which isformed, is of course desirable in relatively large amounts. However, iftoo much of this material is included it will not go in solution so therange indicated cannot be exceeded by very much. Although the shellac isan excellent binder and has its own effect in scale conditioning toomuch of this ingredient can result in carbon deposits on the surface ofthe metal, if it is later subjected to heat, as the shellac burns. Someof these spots can become so severe that removal is impossible. In orderto provide proper saponification for the composition diethylamine shouldbe included approximately as indicated. Above this range no additionalbenefit is obtained although it is possible to include up to aboutpercent by weight without harmful effect.

This composition, when applied to the surface of a workpiece, has inaddition to its scale deterent characteristics' the-ability to act as anextremely effective dry forming lubricant for metal working, which usemay even prove to be more important than that of treating the metal forscale formation. The material provides a very slippery surface for theworkpiece while at the same adhering very tenaciously, and will hold oneven when drawn or pulled into a die. As the part is being formed itappears to provide a cushioning effect which protects the metal and dieand permits the forming to take place. The minute quantity of thematerial which will be rubbed oif as the metal is formed builds upslightly on the die surface thus providing a polishing effect and a moresmooth and effective die is obtained. For its use as a lubricant it ispreferred to spray on two coats of the material prior to the formingoperation so as to provide a relatively thick coat on the part. Afterthe forming operation the material may be left on for further heat treator other work whereby a dual function can be obtained from the material.First it will act as a lubricant in permitting forming of the part, andsecondly will retard scale formation and condition the scale when thepart is subsequently heat treated. However, if it is desired to removethe material immediately after the metal forming this is quite easilyaccomplished due to the water solubility thereof. Mere dipping in waterwill thoroughly cleanse the part without scrubbing. Although it hasprimarily been used for a cold forming lubricant it is also useful inhot forming where it acts as a base for an additional conventionallubricant coating applied at the time the hot forming is to take place.Results for both types of forming are materially improved when the metalsurface is coated. Its use as a forming lubricant is applicable not onlyto titanium and 17-7 PH stainless steel but also toother steels,aluminum and other metals as well.

Several advantages therefore may be listed for the material as a metalforming lubricant. First and foremost it produces superior parts andconsiderably increases die life. The fact that it can be applied beforethe time of forming is an advantage in production and provides aprotection of the part during material handling. Application of thelubricant by spraying means that there is no waste of material and costis much lower than with ordinary lubricants. Furthermore the lubricantmay be retained on the surface part for subsequent heat treating or, ifdesired, it may be removed simply by dipping in water.

A second formulation of the composition of this invention has beensuccessfully carried out and also is quite effective in pretreatment forscale formations as well as a metal lubricant. For the latter purpose,it is primarily for instances where the part will be subsequently subjected to heat to avoid a removal problem. This solution is as follows:

Component: Percent by weight Boric acid, tech. 3.5 to 4 Shellac, orange,four pound cut, Federal Spec. 'IT-V-91B 33 to 50 Dye .05 t9 1.0 Ethylalcohol, Federal Spec. 0-A-396 Balance It maybe noted that the compoundin the second example contains no amine as it is shown. This has one advantage where parts are to be treated and stored for some time prior totheir working or heat treatment. Without the amine the compound is notwater soluble and the moisture in the air will not attack the solutionso that the coating will remain on the part indefinitely. However, if itis desired to provide a water soluble solution, around one percent of anamine added to the above formulation will provide this effect. Note thatthe use of ethyl alcohol means that ethyl borate will be formed when thecompound is made up, this being a non-volatile liquid. Therefore, thereis no problem of loss of the borate as encountered with gaseous methylborate. The propertions of the ingredients should be retainedsubstantially as indicated in the table; boric acid above for percent inthe solution causes it to be somewhat unstable and reduces its shelflife. The larger quantity of shellac used with this modification willsuspend any particles of boric acid that have not gone into solution toassure that an adherent coating is obtained.

Another variation of this compound has been prepared and shown toprovide utility in retarding scale formations, but it is not regarded asquite as effective as the previously given examples. This modificationcomprises one part of b-oric acid suspended in a solution of one partshellac, four parts of methanol and one part isopropanol.

It can be seen from the foregoing that I have provided an improved metaltreating material which has numerous advantages for both of its dualfunctions. Scale formations for titanium and l7-7 PH stainless steel aregreatly reduced while the material offers tremendous advantages as a drylubricant for metal forming.

The foregoing detailed description is to be regarded as given by way ofexample only, the spirit and scope of this invention being limited onlyby the appended claim.

I claim:

A metal treating composition consisting of a solution of substantially7.8 to 8.2 percent by weight boric acid,

4.0 to 4.5 percentflake shellac, 3.3 to 3.5 percent diethylamine, 4.0 to5.0 percent water, and the balance of a material taken from the groupconsisting of ethanol,

methanol and isopropanol.

References Cited in the file of this patent 8 UNITED STATES PATENTS1,896,040 Ruben. Jan. 31, 1933 1,923,058 Lawstuter Aug. 15, 19332,483,598 Schrank Oct. 4, 1949 2,588,234 Hendricks Mar. 4, 19522,762,115 Gates Sept. 11, 1956 FOREIGN PATENTS 151,688 Great BritainSept. 20, 1920 OTHER REFERENCES

